1. Field of the Invention
The present invention relates generally to nuclear fuel pellet diameter inspection, and more particularly, to a pellet reject apparatus and method which operates in conjunction with transfer and laser scanning of pellets to monitor detection of off-size pellets and to effectuate their rapid removal from a pellet production line.
2. Description of the Prior Art
A nuclear fuel pellet having an off-size diameter can greatly affect the efficiency and cost of manufacturing nuclear fuel rods. In particular, a pellet with an oversize diameter may clog the entry to the fuel rod, requiring the operator to turn off the pellet feeding apparatus, pull out the oversize pellet, and/or replace the affected fuel rod. This corrective measure wastes considerable manufacturing time.
Additionally, an oversize fuel pellet can cause premature and costly replacement of a nuclear fuel rod in the reactor core at a nuclear power plant. If a pellet is too large, the pellet-to-clad gap is reduced, leading to excessive clad stresses and potential fuel rod failure during core operation.
A recent pellet inspection system, which is designed to inspect 100% of the pellets moving in a production line, employs a pellet transfer apparatus in conjunction with a laser scanning apparatus for scanning pellets with a laser beam to measure and detect oversize ones as they are moved, arranged end-to-end in a single file row, from the grinding station to a pellet storage tray. The pellet transfer apparatus of this inspection system is the subject of the first patent application cross-referenced above, whereas the laser scanning apparatus of this system is the subject of the second cross-referenced patent application.
In the operation of the aforementioned inspection system, upon detection of an unacceptable, or off-size, pellet, the laser scanning apparatus causes the pellet transfer apparatus to halt. Since the laser scans up to fifteen pellets per second, identification of the offending pellet requires the inspector to manually re-run each of several downstream pellets through the scanner. This procedure results in unacceptable delays in production. The alternative is to manually remove a number of pellets each time the laser halts the flow of pellets. This approach, while reducing downtime, is also unattractive since many pellets must be removed due to uncertainty resulting from the large number of pellets passing the scanner each second.
Consequently, a need exists for a different way to remove off-size pellets so as to avoid the above-mentioned drawbacks.